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| 1 | +// -*- C++ -*- |
| 2 | +//===----------------------------------------------------------------------===// |
| 3 | +// |
| 4 | +// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| 5 | +// See https://llvm.org/LICENSE.txt for license information. |
| 6 | +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| 7 | +// |
| 8 | +//===----------------------------------------------------------------------===// |
| 9 | + |
| 10 | +#ifndef _LIBCPP___CHRONO_UTC_CLOCK_H |
| 11 | +#define _LIBCPP___CHRONO_UTC_CLOCK_H |
| 12 | + |
| 13 | +#include <version> |
| 14 | +// Enable the contents of the header only when libc++ was built with experimental features enabled. |
| 15 | +#if !defined(_LIBCPP_HAS_NO_EXPERIMENTAL_TZDB) |
| 16 | + |
| 17 | +# include <__chrono/duration.h> |
| 18 | +# include <__chrono/leap_second.h> |
| 19 | +# include <__chrono/system_clock.h> |
| 20 | +# include <__chrono/time_point.h> |
| 21 | +# include <__chrono/tzdb.h> |
| 22 | +# include <__chrono/tzdb_list.h> |
| 23 | +# include <__config> |
| 24 | +# include <__type_traits/common_type.h> |
| 25 | + |
| 26 | +# if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) |
| 27 | +# pragma GCC system_header |
| 28 | +# endif |
| 29 | + |
| 30 | +_LIBCPP_BEGIN_NAMESPACE_STD |
| 31 | + |
| 32 | +# if _LIBCPP_STD_VER >= 20 && _LIBCPP_HAS_TIME_ZONE_DATABASE && _LIBCPP_HAS_FILESYSTEM && _LIBCPP_HAS_LOCALIZATION |
| 33 | + |
| 34 | +namespace chrono { |
| 35 | + |
| 36 | +class utc_clock; |
| 37 | + |
| 38 | +template <class _Duration> |
| 39 | +using utc_time = time_point<utc_clock, _Duration>; |
| 40 | +using utc_seconds = utc_time<seconds>; |
| 41 | + |
| 42 | +class utc_clock { |
| 43 | +public: |
| 44 | + using rep = system_clock::rep; |
| 45 | + using period = system_clock::period; |
| 46 | + using duration = chrono::duration<rep, period>; |
| 47 | + using time_point = chrono::time_point<utc_clock>; |
| 48 | + static constexpr bool is_steady = false; // The system_clock is not steady. |
| 49 | + |
| 50 | + [[nodiscard]] _LIBCPP_HIDE_FROM_ABI static time_point now() { return from_sys(system_clock::now()); } |
| 51 | + |
| 52 | + template <class _Duration> |
| 53 | + [[nodiscard]] _LIBCPP_HIDE_FROM_ABI static sys_time<common_type_t<_Duration, seconds>> |
| 54 | + to_sys(const utc_time<_Duration>& __time); |
| 55 | + |
| 56 | + template <class _Duration> |
| 57 | + [[nodiscard]] _LIBCPP_HIDE_FROM_ABI static utc_time<common_type_t<_Duration, seconds>> |
| 58 | + from_sys(const sys_time<_Duration>& __time) { |
| 59 | + using _Rp = utc_time<common_type_t<_Duration, seconds>>; |
| 60 | + // TODO TZDB investigate optimizations. |
| 61 | + // |
| 62 | + // The leap second database stores all transitions, this mean to calculate |
| 63 | + // the current number of leap seconds the code needs to iterate over all |
| 64 | + // leap seconds to accumulate the sum. Then the sum can be used to determine |
| 65 | + // the sys_time. Accessing the database involves acquiring a mutex. |
| 66 | + // |
| 67 | + // The historic entries in the database are immutable. Hard-coding these |
| 68 | + // values in a table would allow: |
| 69 | + // - To store the sum, allowing a binary search on the data. |
| 70 | + // - Avoid acquiring a mutex. |
| 71 | + // The disadvantage are: |
| 72 | + // - A slightly larger code size. |
| 73 | + // |
| 74 | + // There are two optimization directions |
| 75 | + // - hard-code the database and do a linear search for future entries. This |
| 76 | + // search can start at the back, and should probably contain very few |
| 77 | + // entries. (Adding leap seconds is quite rare and new release of libc++ |
| 78 | + // can add the new entries; they are announced half a year before they are |
| 79 | + // added.) |
| 80 | + // - During parsing the leap seconds store an additional database in the |
| 81 | + // dylib with the list of the sum of the leap seconds. In that case there |
| 82 | + // can be a private function __get_utc_to_sys_table that returns the |
| 83 | + // table. |
| 84 | + // |
| 85 | + // Note for to_sys there are no optimizations to be done; it uses |
| 86 | + // get_leap_second_info. The function get_leap_second_info could benefit |
| 87 | + // from optimizations as described above; again both options apply. |
| 88 | + |
| 89 | + // Both UTC and the system clock use the same epoch. The Standard |
| 90 | + // specifies from 1970-01-01 even when UTC starts at |
| 91 | + // 1972-01-01 00:00:10 TAI. So when the sys_time is before epoch we can be |
| 92 | + // sure there both clocks return the same value. |
| 93 | + |
| 94 | + const tzdb& __tzdb = chrono::get_tzdb(); |
| 95 | + _Rp __result{__time.time_since_epoch()}; |
| 96 | + for (const auto& __leap_second : __tzdb.leap_seconds) { |
| 97 | + if (__leap_second > __time) |
| 98 | + return __result; |
| 99 | + |
| 100 | + __result += __leap_second.value(); |
| 101 | + } |
| 102 | + return __result; |
| 103 | + } |
| 104 | +}; |
| 105 | + |
| 106 | +struct leap_second_info { |
| 107 | + bool is_leap_second; |
| 108 | + seconds elapsed; |
| 109 | +}; |
| 110 | + |
| 111 | +template <class _Duration> |
| 112 | +[[nodiscard]] _LIBCPP_HIDE_FROM_ABI leap_second_info get_leap_second_info(const utc_time<_Duration>& __time) { |
| 113 | + const tzdb& __tzdb = chrono::get_tzdb(); |
| 114 | + if (__tzdb.leap_seconds.empty()) [[unlikely]] |
| 115 | + return {false, chrono::seconds{0}}; |
| 116 | + |
| 117 | + sys_seconds __sys{chrono::floor<seconds>(__time).time_since_epoch()}; |
| 118 | + seconds __elapsed{0}; |
| 119 | + for (const auto& __leap_second : __tzdb.leap_seconds) { |
| 120 | + if (__sys == __leap_second.date() + __elapsed) |
| 121 | + // A time point may only be a leap second during a positive leap second |
| 122 | + // insertion, since time points that occur during a (theoretical) |
| 123 | + // negative leap second don't exist. |
| 124 | + return {__leap_second.value() > 0s, __elapsed + __leap_second.value()}; |
| 125 | + |
| 126 | + if (__sys < __leap_second.date() + __elapsed) |
| 127 | + return {false, __elapsed}; |
| 128 | + |
| 129 | + __elapsed += __leap_second.value(); |
| 130 | + } |
| 131 | + |
| 132 | + return {false, __elapsed}; |
| 133 | +} |
| 134 | + |
| 135 | +template <class _Duration> |
| 136 | +[[nodiscard]] _LIBCPP_HIDE_FROM_ABI sys_time<common_type_t<_Duration, seconds>> |
| 137 | +utc_clock::to_sys(const utc_time<_Duration>& __time) { |
| 138 | + using _Dp = common_type_t<_Duration, seconds>; |
| 139 | + leap_second_info __info = chrono::get_leap_second_info(__time); |
| 140 | + |
| 141 | + // [time.clock.utc.members]/2 |
| 142 | + // Returns: A sys_time t, such that from_sys(t) == u if such a mapping |
| 143 | + // exists. Otherwise u represents a time_point during a positive leap |
| 144 | + // second insertion, the conversion counts that leap second as not |
| 145 | + // inserted, and the last representable value of sys_time prior to the |
| 146 | + // insertion of the leap second is returned. |
| 147 | + sys_time<common_type_t<_Duration, seconds>> __result{__time.time_since_epoch() - __info.elapsed}; |
| 148 | + if (__info.is_leap_second) |
| 149 | + return chrono::floor<seconds>(__result) + chrono::seconds{1} - _Dp{1}; |
| 150 | + |
| 151 | + return __result; |
| 152 | +} |
| 153 | + |
| 154 | +} // namespace chrono |
| 155 | + |
| 156 | +# endif // _LIBCPP_STD_VER >= 20 && _LIBCPP_HAS_TIME_ZONE_DATABASE && _LIBCPP_HAS_FILESYSTEM && |
| 157 | + // _LIBCPP_HAS_LOCALIZATION |
| 158 | + |
| 159 | +_LIBCPP_END_NAMESPACE_STD |
| 160 | + |
| 161 | +#endif // !defined(_LIBCPP_HAS_NO_EXPERIMENTAL_TZDB) |
| 162 | + |
| 163 | +#endif // _LIBCPP___CHRONO_UTC_CLOCK_H |
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